Molybdenum synthesis activity

Transition metal complexes are used as catalysts and as reagents in the synthesis of imides. Molybdenum hexacarbonyl activates strained aziridines and allows the nucleophilic attack of caibanions. Intramolecular rearrangement and a final oxidation yields imides completely stereospecifically (equation 59).38> Dicobalt octacarbonyl catalyzes the conversion of 3,7-unsaturated amides to imides in the presence of carbon monoxide (equation 60). ... 

Keywords Fischer-Tropsch Synthesis, Molybdenum, Iron, Activated Carbon, C1-C34 hydrocarbons... 

Kojima et also studied the impact of molybdenum nitride (7-M02N) and molybdenum carbides (o -MoCi x, / -Mo2C) as well as the addition of second component (Co, Cs) on the activities and rates of ammonia synthesis. Their orders in ammonia synthesis activity were / -Mo2C > a-MoCi-x > 7-M02N. The a-MoCi x is unstable in the condition of ammonia s3mthesis. The addition of 2% of Cs and 5%... 

Molybdenum, in the form of Glemser compounds, is also claimed to show synthesis activity at ambient temperature. The compound is made by the reduction of M0O3 with nascent hydrogen to give an air-sensitive compound of formula... 

Except for cobalt systems, other metals also demonstrate activity in the Fischer-Tropsch process. Mo/HZSM-5 turned out to be active in FT synthesis [98], The catalysts were tested at a low H /CO molar ratio 1.0, this composition being typical for biomass gasification. Liquid hydrocarbons obtained on Mo/HZSM-5 at 573 K were presented by alkylaromatics and lower branched and cyclic alkanes. The formation of aliphatic hydrocarbons was close to zero. The gas products included Cj-C alkanes. Higher alcohols and carboxylic acids (C,-Cg) were observed in the aqueous phase. The formation of hydrocarbons on Mo/zeolite is accounted for by the bifunctional zeolite acidity and molybdenum metal activities via alcohols as intermediates. The zeolite Y was also found to be a good support for Mo in the FT reaction. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Molybdenum and tungsten are unique in that they are resistant to sulfur, and, in fact, are commonly sulfided before use. The Bureau of Mines tested a variety of molybdenum catalysts (32). They are moderately active but relatively high temperatures are required in order to achieve good conversion, even at low space velocities. Selectivity to methane was 79-94%. Activity is considerably less than that of nickel. Although they are active with sulfur-bearing synthesis gas, the molybdenum and tungsten catalysts are not sufficiently advanced to be considered candidates for commercial use. 

Abstract For many years after its discovery, olefin metathesis was hardly used as a synthetic tool. This situation changed when well-defined and stable carbene complexes of molybdenum and ruthenium were discovered as efficient precatalysts in the early 1990s. In particular, the high activity and selectivity in ring-closure reactions stimulated further research in this area and led to numerous applications in organic synthesis. Today, olefin metathesis is one of the... 

We will focus on the development of ruthenium-based metathesis precatalysts with enhanced activity and applications to the metathesis of alkenes with nonstandard electronic properties. In the class of molybdenum complexes [7a,g,h] recent research was mainly directed to the development of homochi-ral precatalysts for enantioselective olefin metathesis. This aspect has recently been covered by Schrock and Hoveyda in a short review and will not be discussed here [8h]. In addition, several important special topics have recently been addressed by excellent reviews, e.g., the synthesis of medium-sized rings by RCM [8a], applications of olefin metathesis to carbohydrate chemistry [8b], cross metathesis [8c,d],enyne metathesis [8e,f], ring-rearrangement metathesis [8g], enantioselective metathesis [8h], and applications of metathesis in polymer chemistry (ADMET,ROMP) [8i,j]. Application of olefin metathesis to the total synthesis of complex natural products is covered in the contribution by Mulzer et al. in this volume. 

Copper deficiency in humans and other mammals is characterized by slow growth, hair loss, anemia, weight loss, emaciation, edema, altered ratios of dietary copper to molybdenum and other metals, impaired immune response, decreased cytochrome oxidase activity, central nervous system histopathology, decreased phospholipid synthesis, fetal absorption, and eventually death (NAS 1977 Gallagher 1979 Kirchgessner et al. 1979 USEPA 1980 ATSDR 1990 Percival 1995). 

Non-noble metal molybdenum containing carbonyls were studied for ORR activity.189-191 Mox(CO) and Mo,Sr(C 0) were studied side by side.189 190 These high-nuclearity carbonyl compounds were prepared by sintering. It was found that the Mox(CO) was amorphous by XRD, however, as S was added, a polycrystalline/ amorphous combination was formed in the catalyst. While neither Mox(CO) or Mo SyCO), compounds were found to be very active for ORR, the addition of S to Mox(CO) appeared to nullify any activity towards ORR.189 190 MoxSeJ,(CO) was produced by both screen printing and sintering191 as well as chemical synthesis.192 The screen printed catalysts were more active than the sintered catalysts, but as the amount of Se increased, the ORR activity decreased.191 192... 

Self, W. T., Grunden, A. M., Hasona, A., and Shanmugam, K. T. (1999). Transcriptional regulation of molybdoenzyme synthesis in Escherichia coli in response to molybdenum ModE-molybdate, a repressor of the modABCD (molybdate transport) operon is a secondary transcriptional activator for the hyc and nar operons. Microbiology 145, 41-55. 

Since the late seventies efforts were directed toward the development of well-defined catalysts that would be active without addition of additives or further modification. A wide variety of tungsten and molybdenum alkylidene complexes have been prepared. Many of them show some activity, but only few are good catalysts. The synthesis is often not straightforward and a range of synthetic procedures varying solvents, alkylating reagents, anions, and alkylidene moieties have to be tried before a desired compound will be obtained. 

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